The compounds of the instant invention are members of the class of cyclic compounds designated crown ethers.
The name "crown ether" was given to the class of cyclic compounds containing repeating ethyleneoxy units by Pedersen in 1967. The name derives from the ability of these compounds to "crown" cationic species as a regal crown adorns a monarch's brow. It is presumed in the nomenclature that in the name "wx-crown-yz" crown indicates repeating C--C--O units unless otherwise indicated, wx is a number indicating the total number of atoms contained in the macroring and yz is a number indicating the number of heteroatoms in the ring.
The specific compound, 4,13-diaza-18-crown-6, has been known for some time having been synthesized by Lehn and his coworkers as an intermediate required for the preparation of cryptands. The compound has the structural formula: ##STR1## The method used by Lehn et al. to synthesize the compound is described in U.S. Pat. No. 3,888,877. It was prepared in two steps from triethylene glycol diamine and triglycoyl chloride by condensation under high dilution conditions, followed by reduction of the diamide resulting from this with diborane. Other methods are also available but they involve complicated experimental procedures and/or multistep reaction schemes.
The cation complexing properties of the compounds of this invention make them of value for use in much the same way and for the same purposes as chelating agents. Thus, the cation complexing properties of the compounds render them of value in processes directed to the desalination of brines or to the separation of metals, for example, to the separation of metals such as the transition metals and the actinides from low grade sources of these metals and to subsequently obtaining such metals in high purity form. In this connection, the compounds are considered to be particularly useful in the separation of high cost metals such as those of the platinium group. Compounds such as those described herein also can bind cations in the alkali metal and alkaline earth groups selectively, one over the other.